Fix RTP to hold mutator lock while using raw mirror pointers.
ReferenceTypePropagation::RTPVisitor::SetClassAsTypeInfo()
is taking a raw mirror::Class* parameter, so it must be
marked with SHARED_REQUIRES(Locks::mutator_lock_). The
omission of this annotation allowed
https://android-review.googlesource.com/216926
to compile despite using GC-unsafe raw mirror pointers in
UpdateFieldAccessTypeInfo(). This led to test failures in
the debug-GC mode.
Change-Id: I2a743070c642e7a611480e5d495af44f0945e43f